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BARYTA   (Barium Hydroxide)

Ba(OH)8 + 8HaO= 315-37

Colourless, more or less opaque, lamellar crystals, or white or yellowish
fused masses ; in the crude state it forms more or less grey crystalline
masses. It dissolves in 20 parts of cold, or 2 parts of boiling water, but
complete solution is difficult owing to the presence of insoluble carbonate.
Its impurities may be carbonate, sulphate, sulphide and thiosiilphate of
barium, chlorides, heavy, earthy and alkali metals. Its examination
includes :

1.  Carbonate, Sulphate.'—2-3 grams arc dissolved in dilute hydro-
chloric acid, effervescence indicating carbonate in considerable amount;
insoluble residue may be barium sulphate.

2.  Sulphide.—5 grams are dissolved in excess of hydrochloric acid
and the solution heated, evolution of hydrogen sulphide being tested for
with lead acetate paper ; or, a few drops of lead acetate solution are added
to the aqueous solution and any black precipitate noted.

3.  Sulphite, Thiosiilphate.—5 grams are treated with 50 c.c. of water
and about 0-5 gram of cadmium carbonate   (to eliminate the sulphide),
the liquid being heated for about. 30 minutes on the steam-bath and filtered.
To the nitrate are added a, little starch, paste and then dilute iodine solution ;
in absence of sulphite and thiosiilphate, a. blue coloration appears imme-

4.  Chlorides.—2-3 grams, dissolved in dilute; nitric acid, should not
be rendered turbid by silver nitrate.

5.  Heavy Metals.—The hydrochloric acid solution  is treated with
hydrogen sulphide and then with ammonia and ammonium sulphide;
traces of lead and copper and small proportions of iron arc1, to be; tested for.

6.  Alkaline Earths, Alkalies......-5 grams are dissolved in dilute hydro-
chloric acid, the solution heated and the barium precipitated with sulphuric
acid and filtered.   The filtrate1 should remain clear on addition of alcohol
and should leave no sensible residue on evaporation in a platinum dish.

7.  Quantitative  Determination.   -35 40  grains  of  the.;   baryta  are
dissolved in boiled water and the volume4 made up te> i litre1.    The* following
determinations are made; on aliquot parts etf this solution removed by moans
of a burette with automatic filling device, in order to avoid the action of
atmospheric carbon dioxide.

(a.) Barium hydroxide. 25 c.c. of N/5-hydroehloric acid, plus about
200 c.c. of water and 10-12 drops of 0-5% methyl orange solution, are
titrated with the baryta solution, the point of neutrality being taken as
the change from orange yellow to a distinct yellow. 25 c.c. N/5-HC1 —
07885 gram Bzi(OH)8' + 8HB0.

(b) Hydrogen sulphide and thiosulphuric acid.

(i) 200 c.c. of the baryta solution are acidified with acetic acid in a half-
litre bottle with a ground stopper, a little starch paste being then added
and the liquid titrated with about N/io-iodinc solution. The iodine solu-
tion is previously titrated with N/io-sodium thiosiilphate solution.the determination of the; alcohol. The alcohol by volume multiplied